Hiding MDF joints

mlundy57 · « **on:** 29 May 2013, 01:00 pm »

I have noticed in a number of build threads that it is very difficult to permanently hide the butt joints in MDF. I was wondering if anybody has tried cutting a small grove in each seam with a wedge bit then filling this with thickened epoxy or glazing compound?

jparkhur · « **Reply #1 on:** 29 May 2013, 01:38 pm »

Roll on 1 2 3 primer and I have never had an issue with seeing them. I build a pair of V1 recently and had to add some pieces of mdc, and after primer, could not see the joint at all.

Jon

mlundy57 · « **Reply #2 on:** 22 Aug 2013, 08:10 pm »

Jon,

Do you use the primer under both paint and veneer or just paint?

Mike

jparkhur · « **Reply #3 on:** 22 Aug 2013, 08:18 pm »

Just paint. I don't typically veneer.

mlundy57 · « **Reply #4 on:** 22 Aug 2013, 11:23 pm »

Thanks

Now that I have finished the X-LS & X-CS Encores and haven't started on a pair of X-MTM Encores yet I'm back to experimenting.

Before I decided to build the X-LS & X-CS Encores I had built up 3 other pairs of cabinets: 1 pair started off as an AV-1 but ended up just being a solid box that I have used to practice different types of cuts on, a second is a pair of AV-1 cabinets, and the third is a pair of N-1X cabinets. All of these cabinets are made out of 3/4" MDF.

The solid set is going to be practice with rounding over all edges and painting. One of the other two will be practice with the vertical edges of the front baffle rounded over and the cabinet veneered. I'll decide what to try on the 3rd pair after I'm done with the first two.

Ant suggestions from those who veneer on how to prep the MDF?

Mike

cody69 · « **Reply #5 on:** 22 Aug 2013, 11:48 pm »

Assuming you have good joints and seams all match, veneering doesn't require you to do much prep to the substrate. I will sand it with 80 or 100 grit paper to give the glue some tooth to grab, but that's about it.

Good luck and post your results.

SJ David · « **Reply #6 on:** 23 Aug 2013, 04:16 am »

Quote from: mlundy57 on 29 May 2013, 01:00 pm

I have noticed in a number of build threads that it is very difficult to permanently hide the butt joints in MDF. I was wondering if anybody has tried cutting a small grove in each seam with a wedge bit then filling this with thickened epoxy or glazing compound?

I use Bondo to fill the seems. I wrap full sheets of 80 and 130 grit sand paper around a 2 foot 2x4. This helps prevent uneven sanding. Also, the Bondo is harder than the MDF so it takes time and patience. The seems, especially corners, come out quite nice.

dBe · « **Reply #7 on:** 23 Aug 2013, 04:21 am »

First of all, I don't use standard MDF for cabinets. I use Medex which is an exterior grade MDF, but it is dimensionally stable and does not swell or shrink with moisture. I use Titebond II - a moisture resistant glue that is stable and does not creep or move with humidity or time. the most important thing is to not rush the drying time of the Titebond. I let glued pieces sit for at least 4 days before doing finish sanding of the pieces.

At this point in time it is sand and finish away. Sealing the edge of the medex is a breeze because it is very consistent through the sheet unlike standard MDF.

A couple of things about Medex in addition. It is much denser and stiffer than ROTM MDF. It also does not have the surface fibers that are a nag to remove. Great material.

http://www.plywoodcompany.com/application/home/itemdetails.aspx?categoryid=41&itemid=320

Dave

WireNut · « **Reply #8 on:** 23 Aug 2013, 04:26 am »

West system epoxy will cure all your needs.

mlundy57 · « **Reply #9 on:** 23 Aug 2013, 04:28 am »

I have never seen Medex. Is it readily available or is it something that has to be special ordered?

Mike

mlundy57 · « **Reply #10 on:** 23 Aug 2013, 04:30 am »

WireNut,

You've mentioned the West System epoxy before. Can veneer be applied over the epoxy? How do you apply it smoothly and evenly on all sides, especially with rounded over edges?

Mike

WireNut · « **Reply #11 on:** 23 Aug 2013, 04:36 am »

I see Vapor Audio in the house

You know what I'm talking about. You use West Systems epoxy to build your loudspeakers and you make the most awesome cabinets available.

Vapor Audio · « **Reply #12 on:** 23 Aug 2013, 04:37 am »

It all depends on what your definition of hide is, and on how long of a time horizon.

All the tricks described here, we've used ... none are guaranteed. When we need to be 100% sure that a seam will never pop, we skin the cabinet with formica.

We've used Medex, painted the seams with West Systems epoxy, sanded that and put 3-4 coats of lacquer sanding sealer, sanded that and used high build primer, sanded that and paint ... and STILL had the seams pop.

Bottom line is MDF moves like crazy, even the fancy expensive stuff like Medex will move a lot. Trust me, I've seen a Medex cabinet that was left in the shop literally almost tear itself apart from all the movement, even though it was covered inside and out with epoxy.

WireNut · « **Reply #13 on:** 23 Aug 2013, 04:38 am »

Quote from: mlundy57 on 23 Aug 2013, 04:30 am

WireNut,

You've mentioned the West System epoxy before. Can veneer be applied over the epoxy? How do you apply it smoothly and evenly on all sides, especially with rounded over edges?

Mike

I'm gonna let Vapor Audio take it from here

I'll be back

Vapor Audio · « **Reply #14 on:** 23 Aug 2013, 04:39 am »

Quote from: mlundy57 on 23 Aug 2013, 04:30 am

WireNut,

You've mentioned the West System epoxy before. Can veneer be applied over the epoxy? How do you apply it smoothly and evenly on all sides, especially with rounded over edges?

Mike

Yes, you can veneer over the epoxy ... we do it all the time. Mix some 410 Microlight filler with the epoxy to make it easy to sand, and veneer over it however you like.

WireNut · « **Reply #15 on:** 23 Aug 2013, 04:40 am »

Quote from: Vapor Audio on 23 Aug 2013, 04:37 am

It all depends on what your definition of hide is, and on how long of a time horizon.

All the tricks described here, we've used ... none are guaranteed. When we need to be 100% sure that a seam will never pop, we skin the cabinet with formica.

We've used Medex, painted the seams with West Systems epoxy, sanded that and put 3-4 coats of lacquer sanding sealer, sanded that and used high build primer, sanded that and paint ... and STILL had the seams pop.

Bottom line is MDF moves like crazy, even the fancy expensive stuff like Medex will move a lot. Trust me, I've seen a Medex cabinet that was left in the shop literally almost tear itself apart from all the movement, even though it was covered inside and out with epoxy.

Damn, he's the man

Vapor Audio · « **Reply #16 on:** 23 Aug 2013, 04:43 am »

Quote from: WireNut on 23 Aug 2013, 04:38 am

I'm gonna let Vapor Audio take it from here

I'll be back

Haha, well as much as we love using epoxy for everything, when it comes to hiding seams on painted epoxy it's no miracle cure. Although when we skin with formica, we use epoxy to glue it down because I don't trust contact cement for anything!

WireNut · « **Reply #17 on:** 23 Aug 2013, 04:44 am »

West System Epoxy. It just doesn't get any better

Trust Vapor Audio

Vapor Audio · « **Reply #18 on:** 23 Aug 2013, 04:47 am »

Quote from: WireNut on 23 Aug 2013, 04:40 am

Damn, he's the man

Haha, well thanks but truth is we just don't want something to come back to us down the road because a seam popped. All the complaints I've read about the head on Vanderseen 5a's having cracks along every MDF seam, I just shake my head and say duh. It's like they were just asking for warranty returns.

We've skinned cabinets with .060" sheet aluminum too, and it didn't work very well. Seam pops telegraphed through the aluminum, formica is the answer we've found.

Vapor Audio · « **Reply #19 on:** 23 Aug 2013, 04:48 am »

Quote from: WireNut on 23 Aug 2013, 04:44 am

West System Epoxy. It just doesn't get any better Trust Vapor Audio

You need to add some 403 Microfibers and 410 Microlight filler to your collection

Have you ever tried sanding something with the Colloidal silica filler in it? It'll eat up paper faster than sanding a concrete floor.